Sonochemical synthesis and characterisation of thermoresponsive microgel particles

Thermoresponsive microgel particles of N-isopropylmethacrylamide and N,N′-methylenebisacrylamide were sonochemically synthesised in water containing sodium dodecylsulfate. Fluorescence spectroscopic measurements using the probes, pyrene and 1-pyrene-carboxaldehyde, showed that microgel systems with a higher crosslinker (N,N′-methylenebisacrylamide) percentage had a more rigid structure. It was also found that a higher crosslinker percentage gave a more hydrophobic surface with a greater density of crosslinking whereas a lower crosslinker percentage gave microgel particles with polymer chains extending out from the surface. Electrophoretic mobility measurements indicated that the microgel particles were electrokinetically unstable since the surface layer of the particles only possessed a low charge (reflective of potentials <|25| mV). However, the majority of the systems were sterically stabilised.